Spark plug



Feb. 5, 1935. F. M. ANTHONY 1,989,671

SPARK PLUG Filed Nov.,28, 1931 FIG. I.

INVENTOR FELIX M. ANTHON ATTORNEY Patented F eb. 5, 1935 UNITED STATESPATENT OFFICE SPARK PLUG Felix M. Anthony, Piedmont, Calif., assignor o1one-fourth to Kenneth G. Gillis and one-fourth 3 Claims.

. This invention relates to improvements in spark plugs and moreparticularly to the ground terminals of spark plugs for internalcombustion engines.

The principal object of the invention is to arrange and design theground terminal to compensate for its expansion and contraction tomaintain an accurate spark gap between the electrode terminals at allengine temperatures.

Other objects and advantages appear as the description progresses.

Broadly stated, the invention consists of arranging the ground terminalto form a reverse curve. The two branches of the curve expand andcontract in opposite directions; thus each compensates for the movementsof the other, maintaining the end of the terminal in a fixed positionwith respect to the positive electrode of the spark plug.

In this specification and the accompanying drawing the invention isdisclosed in its preferred form. It is to be understood, however, thatit is not limited to this form because it may be embodied in other formswithin the purview of the claims following the description.

In the one sheet of drawings:

Fig. 1 is a side elevation of a spark plug having electrode terminalsconstructed in accordance with this invention.

Fig. 2 is an end view of the same from below.

Fig. 3 is an enlarged vertical section of the lower portion of the sparkplug diagrammatically showing the directions of the movements of thecurved portions of the ground terminal during expansion.

In detail the construction illustrated in the drawing comprises theouter shell 1 having the threaded neck 2 for engaging the cylinder headof the motor, not shown. The shoulder 3 provides for compressing theusual gasket against the cylinder head when the shell is screwed intoplace by means of the hexagonal portion 4.

The center bore of the top portion of the shell is internally threadedto receive the bushing 5, having the hexagonal head 6.

The dielectric core 7 is usually formed of porcelain, compressed mica,or other refractory insulating material. This core extends through theshell 1 and is held in fixed position by screwing down the bushing 5which forces the core against a suitable shoulder provided within theshell 1.

The center electrode 8 extends entirely through the core and is threadedat its upper end to engage the conventional terminal coupling 9. The

REESSUED lower end of the electrode projects through the core '7 andterminates in the fiat end 10 beyond the edge of the shell.

The structure thus far described is the construction of the conventionalspark plug, the mechanical characteristics of which will vary With thetype of motor in which it is used. It will be obvious to those skilledin the art that the present invention may be applied with suitablemodifications to any of the existing types of 10 spark plugs.

The superiority of spark plugs in which the spark gap is locatedcoincidentally with the axis of the spark plug has been long recognizedby the art. However, it has been found to be impractical to use thistype of spark plug due to variations in the length of the spark gapunder varying temperatures. In prior constructions having this type ofspark gap, the ground terminal is fixed in the outer shell andinvariably has a single bend to bring the end of the terminal intoproximity with the center electrode. As the spark plug becomes heated,the bent portion of the ground terminal tends to partially straightenout, thus greatly increasing the length of the spark gap. This preventsa sufiicient volume of current bridging the gap to form the hot sparknecessary in modern internal combustion motors.

It is the purpose of the present invention to render practical the useof spark plugs having a spark gap located coincidental with the axisthereof. This is accomplished by designing the ground terminal tomaintain an accurate spark gap at all temperatures of engine operation.

The ground terminal 11, provided by this invention, is fixed at 12 tothe edge of the shell 1 and is bent at 13 toward the center electrodeforming a semicircular arc. The terminal is bent in the oppositedirection at 14 to form an are joining the arc 13 at 15 to form areverse curve. The are 14 has a shorter radius than the arc 13, theratio of the two radii being substantially two to one.

The end portion 16 of the terminal extends tangentially from the are 14and lies in juxtaposition with the end of the center electrode leavingthe spark gap 18 of the usual clearance. The terminal end 16 ispreferably partially flattened to form a plane parallel with the fiatend 10 of the electrode to increase the sparking area. It is desirablethat the flattening 16 should be so performed to leave the fillet 19 toreinforce the arc 14.

The lower portion of the bent terminal should be located below theterminal end 16 to drain away any accumulations of oil from the sparkgap.

As the engine becomes heated, the 'arc 13 in the ground terminal expandsand begins to straighten out in the direction of the arrow :1; (see Fig.3). However, the are 14 expands and straightens out intheoppositedirection as'indicated by the arrow 1: and compensates for theexpansion of the are 13, thus maintaining the terminal end 16 in fixedposition with respect to the end of the center electrode. 7 7

To secure perfeet compensating expansion action of the ground terminalit is important that the approximate proportions of the branches of thereverse curve be maintained in manufacture.

The longer radius and length of the are 13 is determined several factorsin the operation of the spark plug. 1

It is to;be noted that the temperature of the ground terminal variesthroughout its length. The heat of the portion forming the are 13 islargely conducted away through the adjacent shell 1 into the largerrelatively cool body of the cylinder head. The are 14 being adjacent theintense heat of the spark reaches a greatlyl'higher temperature than theare 13. This requires the are 13 to be of larger radius and length toincrease the distance of its expansion to compensate for the greaterangular expansion of the more heated 81p 14. i

n The partial flattening pf the terminal end 16 also reduces thethickness of the terminal 11 at the are 14. As this flattening of thecross section at the are further increases its angular expansion, itprovides further necessity for the larger size of the are 13.

Having thus described this invention, what I claim and desire to secureby Letters Patent is:

1. A spark plug having ashell; an insulated electrode in said shell; anda ground terminal having one end fixed in said shell and its free end injuxtaposition to said electrode to form a spark gap of predeterng inedwidth the ground terminal being bent into ajreverse curve with unequalradii, the greater radius being adjacent said shell, the cross sectionof said terminal being flattened transversely to the plane of the radiusof the curve adjacent said electrode, all combined and arranged tomaintain substantially the predetermined t idth of said spark gap underworking temperature variations.

i 2. A spark plug having a shell, an insulated electrode in said shell,a ground terminal, bent in ;a reverse curve and having its free endp'girtion in juxtaposition with said electrode to form a spark gap ofpredetermined width, the radius of the curve adjacent the shell beinggreater than the radius adjacent the electrode, said curves beingproportioned one to the other to maintain said spark gap the samerelative width under various working temperature variations;

3. Aspark plug having a shell, an insulated electrode in said shell, aground terminal bent in a reverse curve and having one end fixed in saidshell and its free'end arranged in a plane substantially parallel withthe plane of the end of said electrode to form 'a spark gap ofpredetermined width, the radius of the curve adjacent the shell beinggreater than the radius adjacent the electrode, said curves beingproportioned one to the other to maintain said spark gap the samerelative width under various working temperature variations.

FELIX M. ANTHONY.

